Provides a number of user-level functions to work with "grid" graphics, notably to arrange multiple grid-based plots on a page, and draw tables.
提供一些用户级别的函数来处理“网格”图形，特别是在页面上安排多个基于网格的绘图，并绘制表格。

基础使用
basic usage
In this example we mix a few grobs and plots.

library(gridExtra)
library(grid)
library(ggplot2)
library(lattice)

p <- qplot(1,1)
p2 <- xyplot(1~1)   ##lattice包

r <- rectGrob(gp = gpar(fill = "grey90"))   ##rectGrob
t <- textGrob("text") 

grid.arrange(t,p,p2,ncol = 2)

Title and/or annotations

gs <- lapply(1:9, function(ii)
    grobTree(rectGrob(gp = gpar(fill = ii,alpha = 0.5)),textGrob(ii)))

# gs
grid.arrange(grobs = gs,ncol = 4,top = "top label",bottom = "bottom\nlabel",left = "left label",right = "right label")

grid.rect(gp = gpar(fill = NA))  ##外边框

Complex layouts
复杂布局
We can provide a matrix defining the layout
使用矩阵定义一个布局

lay <- rbind(c(1,1,1,2,3),
             c(1,1,1,4,5),
             c(6,7,8,9,9))

grid.arrange(grobs = gs,layout_matrix = lay)

The layout itself may contain holes,but note that for any given grob index the region must be simply connected(no hole)

hlay <- rbind(c(1,1,NA,2,3),
              c(1,1,NA,4,NA),
              c(NA,7,8,9,NA))

select_grobs <- function(lay) {
  id <- unique(c(t(lay)))
  id[!is.na(id)]
}

grid.arrange(grobs=gs[select_grobs(hlay)], layout_matrix=hlay)

All cells are of equal size by default, but users may pass explicity widths and/or heights in any valid grid units, or as relative numbers (interpreted as null)

grid.arrange(grobs = gs[1:3],ncol = 2,widths = 1:2,heights = unit(c(1,10),c("in","mm")))

Nested layouts with arrangeGrob
The grid.arrange() function draws on the device;for more complex layouts,we may want to store the gtable and combine it with other objects,e.g.forming nested layouts.To this end,usearrangeGrob().

g1 <- arrangeGrob(grobs = gs,layout_matrix = t(lay))
g2 <- arrangeGrob(grobs = gs,layout_matrix = lay)
grid.arrange(g1,g2,ncol = 2)

Multiple pages output
Finally, we may want to place grobs on multiple pages; the marrangeGrob() function provides a convenient interface for this, also compatible with ggsave().

set.seed(123)
pl <- lapply(1:11,function(.x)
  qplot(1:10,rnorm(10),main = paste("plot",.x)))

ml <- marrangeGrob(pl,nrow = 2,ncol = 2)
ml

Regular polygons and ellipses in grid graphics
多边形和椭圆

N <- 5
xy <- polygon_regular(N)*2

# draw multiple polygons
g <- ngonGrob(unit(xy[,1],"cm") + unit(0.5,"npc"),
              unit(xy[,2],"cm") + unit(0.5,"npc"),
              n=seq_len(N)+2, gp=gpar(fill=1:N))


grid.newpage()
grid.draw(g)

Rotated and stetched polygons

g2 <- ngonGrob(unit(xy[,1],"cm") + unit(0.5,"npc"),
              unit(xy[,2],"cm") + unit(0.5,"npc"),
              n=seq_len(N)+2, ar=seq_len(N),
              phase=0, angle=pi/(seq_len(N)+2),
              size=1:N+5, gp=gpar(fill=1:N))

grid.newpage()
grid.draw(g2)

Ellipses

g3 <- ellipseGrob(unit(xy[,1],"cm") + unit(0.5,"npc"),
                  unit(xy[,2],"cm") + unit(0.5,"npc"),
                  angle=-2*seq(0,N-1)*pi/N+pi/2,
                  size=5, ar=3, gp=gpar(fill=1:N))

grid.newpage()
grid.draw(g3)